Birmingham ran out 2-0 winners.
Birmingham manager Alex McLeish saluted his players after the team took over at the top of the Coca-Cola Championship.
First-half goals from Kevin Phillips and Garry O'Connor extended Birmingham's 100% start to the season and sentenced Barnsley to a fourth straight defeat.
McLeish said: "It was a very satisfying three points. We knew that there would be some pressure on us playing at home.
"But the players were able to deal with that and it is good that we have been able to keep our momentum going.
"Barnsley did make it difficult for us at times and they had a couple of chances but the defence did well and Maik Taylor did a great job in goal.
"In terms of the points we have picked up I can't ask any more from the players than to have collected maximum points.
"But I do think that there is still more to come from us and that we can get better."
Phillips made Birmingham's early pressure pay when he ghosted in at the far post in the 13th minute for his third goal in three games.
Barnsley failed to fully clear a James McFadden corner and the loose ball found its way to Stuart Parnaby.
He delivered a a perfect cross that Phillips met at the far post with a close-range header.
McFadden then missed an excellent chance to increase Birmingham's lead in the 17th minute when he fired wide.
Barnsley had rarely been seen as an attacking threat in the opening half but they were just inches away from an equaliser five minutes before half-time.
Diego Leon, who had been picked out by a Martin Devaney pass, rattled the Birmingham bar from 25 yards.
That let-off sparked Birmingham back into life and they made the game safe in first-half stoppage time when Barnsley were undone from the left-wing.
Quincy Owusu-Abeyie sent over a cross that goalkeeper Luke Steele failed to deal with and O'Connor was on hand to head home from close range for his second successive strike.
Barnsley boss Simon Davey, whose side were denied a route back into the game when Maik Taylor saved from skipper Brian Howard, hopes better times are just around the corner.
He said: "This is the first time that I have lost four games in a row and it has got to stop now.
"Silly basic errors are costing us and that is why we were behind at half-time.
"We had chances but we didn't take them and that has to change.
We are just not converting them they come along and if that happens things become a struggle.
"Goals change games and the fact that Birmingham scored their second just before half-time changed the game.
"We have now got a massive home game coming up against Derby County next weekend.
"We have got to get three points. The players know that. We know that as staff and the supporters know that. That work begins on Monday morning."